Conventional methods for hydrophilizing the surfaces of materials include (1) applying a surfactant, (2) applying a water absorbing resin, (3) applying a hydrophilic photocatalyst, (4) forming either an inorganic coating by enameling or ceramic thermal spraying, or a silica film, and (5) mixing a hydrophilic component with a resin coating agent. For example, Japanese Unexamined Patent Application, First Publication No. 2000-191960 discloses a hydrophilic coating that uses a photocatalyst.
However, films formed by these methods suffer from a number of drawbacks, including poor durability with respect to detergents.
In other words, in the method (1), which involves applying a surfactant, because the surfactant is water soluble, the effect is lost within a short period of time in the presence of water or detergents. In the method (2), which involves applying a water absorbing resin, the resin is acidic, and consequently degrades in the presence of alkaline detergents. In the method (3), which involves applying a hydrophilic photocatalyst, satisfactory effects cannot be achieved in darker locations, and moreover, the silica binder used to fix the photocatalyst is alkaline, and degrades in the presence of neutral detergents. In the method (4), which involves forming an inorganic coating, only heat resistant materials can be treated by enameling or thermal spraying, and the resulting coatings also display poor impact resistance. Furthermore, silica films degrade in the presence of neutral or alkaline detergents. In the method (5), which uses a resin coating agent, the resin degrades in the presence of acidic or alkaline detergents.
The present invention takes the above problems into consideration, with an object of providing a hydrophilic film which displays excellent hydrophilicity, and also displays excellent durability with respect to acidic, neutral, and alkaline detergents and chemicals.